This invention relates to an engine speed control and more particularly to an improved control for the engine idle speed and also to a throttle control for improving the control of the air flow to an engine.
As is well known, the speed of an internal combustion engine is generally controlled by controlling the amount of air that is supplied to the engine during its running. Normally, a throttle valve is provided for controlling this air flow in spark-ignited engines. The type of throttle valve most conventionally employed is the so-called "butterfly" type of throttle valve. With this type of throttle valve, the generally circular plate-type throttle valve is affixed to a throttle valve shaft that extends across the induction passage and controls the degree of air flow by its rotary or angular position.
The amount of fuel supplied to the engine is varied generally in response to the amount of air supplied. The amount of air flowing to the engine may be determined in a number of ways. For example, throttle position sensors are frequently employed so as to provide an indication of the throttle valve position and, accordingly, the amount of air flow to the engine. Alternatively, actual air flow sensors may be employed.
The amount of fuel supplied is then varied in response to the air flow so as to provide the desired fuel-air ratio for a given running condition. This type of control is particularly employed in conjunction with fuel injection systems wherein the amount of fuel injected may be controlled by methods other than the pressure difference across the fuel discharge circuits, as is the case with carbureted engines.
One particularly sensitive running condition for engines is the idle operation. Normally, the idle speed is controlled by controlling the idle position of the throttle valve. In conventional engines the throttle valve is rotatably positioned in the induction passage so that it lies at an angle of approximately 14 degrees (14.degree.) to a plane passing through the rotational axis of the throttle valve and extending generally perpendicularly to the flow path through the portion of the induction passage in which the throttle valve is positioned. There are a number of disadvantages with this type of arrangement.
The first of these disadvantages is that at this degree of throttle valve position, incremental changes in the angular position of the throttle valve do not result in linear changes in the air flow. This condition may be best understood by reference to FIGS. 1 and 2. FIG. 1 shows the air flow through the induction passage in response to the degree of opening of the throttle valve from its fully closed position. As may be seen, during the idle and low-speed range, indicated by the area bracketed at A, for a given degree of throttle valve opening in this range, there is a significantly different degree of air flow.
The reason for this may be understood by reference to FIG. 2 in which the solid-line view is an expanded view showing the effective induction passage flow area in response to a given throttle valve position. The point indicated at I is the normal idle position of the throttle valve. As may be seen, the curve of the throttle valve opening has a slope .theta.2 at this point, which is relatively great. As a result, a small degree of change in throttle valve opening provides a large change in effective flow area. Thus if fuel amount is controlled by throttle valve position, a non-linear fuel/throttle valve position curve must be employed. Furthermore this condition continues to progress as the throttle valve is opened to an off-idle condition, indicated at B.
If, rather than controlling the degree of idle air flow by positioning the throttle valve in such an open condition as the 14 degree position as in the prior art construction, it is possible to maintain the throttle valve in a substantially closed position and provide the air flow through an independent source, then a curve as shown in phantom lines in FIG. 2 can result. With such an arrangement, the change in slope of the curve as the throttle valve is opened from its fully closed position is lower, and the air flow variations will be more uniform and linear. Thus the amount of fuel supplied in response to throttle valve position can be varied in a more linear manner. This permits better idle speed control as well as better fuel economy and emission control.
It is, therefore, a principal object of this invention to provide an improved idle control arrangement for an internal combustion engine.
It is a further object of this invention to provide an improved flow controlling throttle valve arrangement for an engine wherein the throttle valve is maintained in a closed position at idle and the air flow is provided independently of the position of the throttle valve for idle operation so as to maintain a more uniform off-idle operation and better idle speed control.
It is a further object of this invention to provide an improved arrangement wherein the idle speed and fuel supply amount can be accurately controlled by minute movements of the throttle valve from its fully closed position if additional air flow is required.
In addition to the defects noted, it has also been found that air flow meters are capable of sensing variations in air flow better if the initial opening of the throttle valve is smaller. That is, the air flow through the intake passage can be more easily measured, particularly with minute variations, when the degree of throttle valve opening is smaller.
Although it would appear obvious from the foregoing description to provide an arrangement wherein the throttle valve is fully closed and extends at a perpendicular relationship to the intake passage at idle, this is not necessarily the optimum condition, as has been found. The reason for this is that the shape of the peripheral edge of the throttle valve must be accurately controlled so as to avoid a biting or digging-in action when opening from this position.
It is, therefore, a still further object of this invention to provide an improved throttle control valve arrangement for an engine wherein the throttle valve is positioned at a relatively small angle to the perpendicular in the idle condition and wherein the throttle valve substantially closes the air flow through the intake passage in this condition.